Insertion Sort List

Problem: Insertion Sort List

The explanation of insertion sort can be found here

Code in Python:

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution(object):
    def insertionSortList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        dummy = insert = ListNode(0)
        while head:
            if insert and insert.val > head.val:
                insert = dummy
            tmp = head.next
            while insert.next and head.val > insert.next.val:
                insert = insert.next
            head.next, insert.next = insert.next, head
            head = tmp
        return dummy.next

An important optimization is that when we get a big node which will be definitely inserted at last, we don't need to scan through the whole list to find a position.